Exemplary embodiments of the present disclosure relate to a sealing structure for a turbine, and more particularly, to a sealing structure for a turbine, capable of maintaining the sealing force of a bucket tip portion, regardless of axial movement of a rotary body, by improving the structure of a brush seal and a labyrinth seal, which are disposed in a stationary body, and the shape of the contact portion of the bucket tip portion which is disposed in the rotary body.
In general, turbines are power generation apparatuses which convert heat energy of fluid such as gas or steam into rotational force as mechanical energy, and each includes a rotor having a plurality of buckets to axially rotate by fluid and a casing which is installed to surround the rotor and has a plurality of diaphragms.
Among these turbines, a gas turbine includes a compressor section, a combustor, and a turbine section. In the gas turbine, outside air is introduced and compressed by the rotation of the compressor section and is then transferred to the combustor, and combustion is performed by the mixture of compressed air and fuel in the combustor. High-temperature and high-pressure gas generated by the combustor drives a generator by rotating the rotor of the turbine while passing through the turbine section.
In a steam turbine, a high-pressure turbine section, an intermediate-pressure turbine section, and a low-pressure turbine section are interconnected in series or in parallel to rotate a rotor. When the high-pressure turbine section, the intermediate-pressure turbine section, and the low-pressure turbine section are interconnected in series, these share one rotor.
In the steam turbine, each turbine has a diaphragm and a bucket with the rotor in a casing interposed therebetween. Steam rotates the rotor while passing through the diaphragm and the bucket, thereby enabling a generator to be driven.
Since each of the gas turbine and the steam turbine has a structure in which a rotary body (a bucket) is rotated relative to a stationary body (a diaphragm), a high-temperature and high-pressure fluid leaks into a gap between the stationary body and the rotary body and such fluid leakage causes the deterioration of energy efficiency due to a power loss. Accordingly, efforts for reduction in fluid leakage occurring in the gap between the rotary body and the stationary body are consistently conducted.
The gap between the rotary body and the stationary body is first decreased to reduce the fluid leakage, but there are various limits in decreasing the gap.
For example, when the gap is too small, vibration is caused by rubbing due to the interference between the rotary body and the stationary body when the rotary body axially rotates, resulting in serious damage to the turbine.
Meanwhile, since the rotary body and the stationary body are heated by hot steam introduced from the boiler in the steam turbine, the rotary body and the stationary body are expanded or contracted from several mm to several tens of mm according to positions thereof when the steam turbine is operated or stopped. In this case, the rotary body and the stationary body are differently expanded because of being made of different materials, and are expanded in different directions according to the structure of the turbine. For this reason, rubbing occurs due to the interference caused while the rotary body and the stationary body are operated.
FIGS. 1A to 1C illustrate a sealing structure between a bucket tip portion of a rotary body and a casing of a stationary body 1 in the related art. Various efforts have been attempted for a long time in order to enhance the sealing between the stationary body 1 and the rotary body. As a result, the arrangement of a labyrinth seal and the shape of a bucket tip portion are changed.
First, referring to FIG. 1A, the bucket tip portion 5 forms a flat portion, and the stationary body 1 has a sealing structure in which a support 2 for fixing a brush seal 4 is disposed at the central portion of the stationary body and labyrinth seals 3 are disposed at both sides of the stationary body. This structure may not prevent the leakage of fluid when the bucket tip portion 5, the labyrinth seals 3, and the brush seal 4 are dislocated due to the excessive axial movement of the rotary body.
In addition, referring to FIG. 1B, the bucket tip portion 5 forms a protrusion portion as another shape, and the stationary body 1 has a sealing structure in which a brush seal 4 is disposed at the central portion of the stationary body and labyrinth seals 3 are disposed at both sides of the stationary body. Similarly, this structure may not prevent the leakage of fluid when the bucket tip portion 5, the labyrinth seals 3, and the brush seal 4 are dislocated due to the excessive axial movement of the rotary body. Moreover, the tooth portions of the labyrinth seals 3 may be damaged due to the collision with the protrusion portion of the bucket tip portion 5.
FIG. 1C illustrates a structure in which tooth portions 7 of labyrinth seals are disposed at the bucket tip portion 5 in order to improve the damage of the labyrinth seals 3 illustrated in FIG. 1B. In this case, when the rotary body excessively axially moves, both of the brush seal 4 and the tooth portions 7 of the labyrinth seals may be worn or damaged due to the collision therebetween. This may deteriorate sealing force in the long time and may ultimately cause the deterioration of turbine power.